1. Technical Field
The present invention relates generally to a mechanism for regulating a draft in a flue, and more particularly toward a mechanism for controlling a rotary gate in a draft regulator.
2. Background Art
It is known to control a flow of gas through a conduit or flue to improve the efficiency with which combustion takes place in an associated gas burner, furnace, or the like. A rotary gate commonly is pivoted in the conduit about an off-center axis on the gate whereby a pressure differential across the gate is effective to rotate the gate and create an axial opening in the conduit for effecting a flow of gas.
Prior art devices control rotation of a gate by applying a torque to the gate in opposition to rotation induced by a pressure differential. For instance, in U.S. Pat. No. 2,650,029 to Field, issued Aug. 25, 1953 (see FIG. 1), an auxiliary weight 14 is suspended by a bead chain 17 from a control gate in a conduit 3. When the control gate 5 is rotated, the bead chain 17 wrappingly engages a cam shaped member 25 on the control gate to apply a variable torque tending to close the control gate. The closing torque varies according to the locations at which the bead chain applies force to the cam shaped member 25 and the control gate 5 relative to the axis about which the control gate rotates.
The use of a flexible member to suspend an adjustment weight from a flow regulating gate wherein the member engages an arcuate camming surface and applies a variable closing torque is shown also, for example, by Field in U.S. Pat. Nos. 2,818,216, issued Dec. 31, 1957.
A problem which exists with draft regulators of the type disclosed in the '029 and '216 patents is the difficulty and cost of manufacturing a camming member which provides desired control over the torque applied to a rotary gate. As a result, controlling the resulting relationship between the impressed (or otherwise unregulated) draft and the regulated draft is difficult.
More particularly, and as indicated previously, draft regulators which have an adjustment weight suspended by a flexible member for engaging a camming surface exert a torque which varies according to both the amount the gate is rotated and the particular shape of the camming surface. In order to provide an acceptable level of control over a draft, it is required to accurately prescribe the amount of torque which is applied to a gate over the entire range of motion of the gate. The present invention is directed toward overcoming the problem of adequately controlling a rotary gate in a draft regulator.